In computer networking a routing table, or Routing Information Base (RIB), is an electronic table (file) or database type object that is stored in a router or a networked computer. The routing table stores the routes (and in some cases, metrics associated with those routes) to particular network destinations. This information contains the topology of the network immediately around it. The construction of routing tables is the primary goal of routing protocols and static routes.
Routing tables are generally not used directly for packet forwarding in modern router architectures; instead, they are used to generate the information for a smaller forwarding table which contains only the routes which are chosen by the routing algorithm as preferred routes for packet forwarding, often in a compressed or pre-compiled format that is optimized for hardware storage and lookup. The remainder of this article will ignore this implementation detail, and refer to the entire routing/forwarding information subsystem as the "routing table".
A routing table utilizes the same idea as one would when using a map in package delivery. Whenever a node needs to send data to another node on a network, it needs to know where to send it. Whenever a device cannot directly connect to the destination node, it needs to find another way to send the package. Whenever a node does not know how to send the package it sends an IP packet to a gateway in the LAN. Since this is a complicated task to route the package to the correct destination, a gateway needs to keep track of the way to deliver this. A Routing Table is the way in which this data is stored, like a map. It is a database which keeps track of paths like a map and provides this information to the node requesting the data. Current router architecture separates the Control Plane function of the routing table from the Forwarding Plane function of the forwarding table [1]
Hop-by-hop routing, each routing table lists, for all reachable destinations, the address of the next device along the path to that destination; the next hop. Assuming that the routing tables are consistent, the simple algorithm of relaying packets to their destination's next hop thus suffices to deliver data anywhere in a network. Hop-by-hop is the fundamental characteristic of the IP Internetwork Layer [2] and the OSI Network Layer, in contrast to the functions of the IP End-to-End and OSI Transport Layers.
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http://en.wikipedia.org/wiki/Routing_table
